Apparatus for supporting creation of access path from host to logical volume

ABSTRACT

A path creation support apparatus acquires either a portion of the parameters required for path creation or parameter decision information for deciding this portion of the parameters from a storage system or a host. The path creation support apparatus decides the portion of the parameters based on the parameter decision information. Upon receiving an access path creation start request, the path creation support apparatus sends an access path creation indication to the host and the storage system which specifies the parameters together with the access path creation start request, and either the parameters acquired beforehand or the acquired parameters decided based on the parameter decision information.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/068,217, filed Feb. 4, 2008, which relates to and claims the benefitof priority from Japanese Patent Application No. 2007-314575, filed Dec.5, 2007, the entire disclosure of which is incorporated herein byreference.

FIELD OF INVENTION

The present invention relates to technology for creating an access pathfrom a host to a logical volume inside a storage system.

BACKGROUND

Japanese Patent Laid-Open No. 2007-233901 discloses technology by whicha management server, which is connected to a host computer (hereinafter,“host”), and a storage system create a path (hereinafter an “accesspath”) from the host to a logical volume provided by the storage system.

Normally, a user must input various parameters into the host to createan access path (to include changing to the newly-created access path).As parameters that have to be inputted to the host, for example, thereare the parameters (for example, a LUN (Logical Unit Number), port ID,logical volume ID, and so forth) for specifying the access path (eitherthe newly created access path or the change-targeted access path).Further, when the storage system is accessed by a plurality of hosts, aparameter that must be inputted is information showing the host storagedomain to which the newly created access path belongs. Decidingappropriate values for each of these various parameters, and inputtingthese values into the host is an arduous task for the user.

Further, changing an access path must be carried out in a state in whichthe access path targeted for this change is not being utilized.Therefore, it is preferable that the user check the utilization statusof the access path targeted for change when changing the access path sothat the access path change can be carried out normally. However, thejob of checking the utilization status of an access path is atroublesome task for the user.

SUMMARY

Accordingly, an object of the present invention is to reduce the burdenon the user when creating an access path.

A path creation support apparatus acquires either a portion of theparameters required for path creation or parameter decision informationfor deciding this portion of the parameters from a storage system or ahost. The path creation support apparatus decides the portion of theparameters based on the parameter decision information. Upon receivingan access path creation start request, the path creation supportapparatus sends an access path creation indication to the host and thestorage system which specifies the parameters together with the accesspath creation start request, and either the parameters acquiredbeforehand or the acquired parameters decided based on the parameterdecision information.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an example of the constitution of a computersystem related to this embodiment;

FIG. 2 is a diagram showing an example of the constitution of a storagesystem;

FIG. 3 is a diagram showing an example of an HSD management table;

FIG. 4 is a diagram showing an example of a VOL management table;

FIG. 5 is a diagram showing an example of an AP run status managementtable;

FIG. 6 is a diagram showing an example of an AP run configurationmanagement table;

FIG. 7 is a flowchart showing the entire flow of processing for creatinga new access path;

FIG. 8 is a flowchart of an HSD detection process;

FIG. 9 is a flowchart of a logical VOL detection process;

FIG. 10 is a flowchart showing the entire flow of processing forchanging an existing access path to a newly created access path;

FIG. 11 is a flowchart of an AP run status check process; and

FIG. 12 is a diagram illustrating an HSD (Host Storage Domain).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In a first embodiment, a path creation support apparatus, which is anapparatus for supporting the creation of an access path from a host tothe logical volume inside a storage system, comprises a groupinformation acquisition unit; a group information storage unit; and apath creation indication unit. A plurality of the access paths isgrouped together on the basis of the type of OS (Operating System) ofthe host that utilizes the access paths. The group informationacquisition unit acquires, from the storage system, group informationshowing the group to which the access path utilized by the host belongs.The group information storage unit stores the acquired groupinformation, and the type of OS of the host, which is associated withthe acquired group information. The path creation indication unit, uponreceipt of an access path creation start request, acquires, from thegroup information storage unit, group information associated with thetype of OS of the host which is to carry out the access path creation,and sends to the host and the storage system an access path creationindication which specifies a parameter specified together with theaccess path creation start request, and the acquired group information.

In a second embodiment according to the first embodiment, the pathcreation support apparatus further comprises a logical volumeinformation acquisition unit; a logical volume information storage unit;and a logical volume decision unit. The logical volume informationacquisition unit acquires, from the storage system, logical volumeinformation showing respective logical volumes that can be provided tothe host by the storage system, and the residual capacities of therespective logical volumes. The logical volume information storage unitstores the acquired logical volume information, and the residualcapacities of the logical volumes associated with the acquired logicalvolume information. The logical volume decision unit decides the logicalvolume to be allocated to a created access path based on the residualcapacities of the respective logical volumes stored in the logicalvolume information storage unit. The access path creation indicationfurther specifies logical volume information showing the logical volumedecided by the logical volume decision unit.

In a third embodiment according to the second embodiment, the logicalvolume decision unit decides the logical volume for which the logicalvolume residual capacity is the largest of the logical volumes stored inthe logical volume information storage unit as the logical volume to beallocated to a created access path.

In a fourth embodiment according to the second embodiment, the logicalvolume decision unit decides the logical volume for which the logicalvolume residual capacity is the closest to a pre-set threshold of thelogical volumes stored in the logical volume information storage unit asthe logical volume to be allocated to a created access path.

In a fifth embodiment according to any of the first through the fourthembodiments, the access path creation start request is a request tostart the change of the access path. The path creation support apparatusfurther comprises an application information acquisition unit;application information storage unit; and path-change-time decisionunit. The application information acquisition unit acquires, from thehost, access information showing whether or not an application, whichruns on the host and uses the access path to access a logical volume, isaccessing the logical volume by utilizing a change-targeted access path,and continuously-running information showing whether or not theapplication is running continuously. The application information storageunit stores the access information and the continuously-runninginformation associated with the application. The path-change-timedecision unit, upon receipt of an access path change start request,references the access information and the continuously-runninginformation associated with the application running on the host that isto carry out the access path change, and when the application isaccessing the logical volume by utilizing the change-targeted accesspath and the application is not the continuously-running application,the path-change-time decision unit stands by until the accessing of thelogical volume by the application utilizing the change-targeted accesspath ends, and causes the path creation indication unit to carry out anaccess path change indication subsequent to the end of the accessing ofthe logical volume utilizing the change-targeted access path.

In a sixth embodiment according to any of the first through fifthembodiments, the access path creation start request is a request tostart the change of the access path. The path creation support apparatusfurther comprises an application information acquisition unit;application information storage unit; and alternative path switchoverindication unit. The application information acquisition unit acquires,from the host, access information showing whether or not an application,which runs on the host and uses the access path to access the logicalvolume, is accessing the logical volume by utilizing a change-targetedaccess path, continuously-running information showing whether or not theapplication is running continuously, and alternative path informationshowing whether or not there is an alternative path for the access pathutilized by the application. The application information storage unitstores the access information, the continuously-running information, andthe alternative path information associated with the application. Thealternative path switchover indication unit, upon receipt of an accesspath change start request, references the access information, thecontinuously-running information, and the alternative path informationassociated with the application running on the host that is to carry outthe access path change, and when the application is accessing thelogical volume by utilizing the change-targeted access path, theapplication is the continuously-running application, and there is analternative path to the change-targeted access path, causes the pathcreation indication unit to carry out an access path change indicationsubsequent to indicating to the host to switch the access path from thechange-targeted access path to the alternative path, and indicates tothe host to switch the access path from the alternative path to apost-change access path subsequent to the access path change ending.

At least one of the respective units described above (the groupinformation acquisition unit, group information storage unit, pathcreation indication unit, logical volume information acquisition unit,logical volume information storage unit, logical volume decision unit,application information acquisition unit, application informationstorage unit, path-change-time decision unit, and alternative pathswitchover indication unit) can be constructed from hardware, a computerprogram, or a combination thereof (for example, one part can be realizedvia a computer program, and the remainder can be realized via hardware).The computer program is executed by being read into a prescribedprocessor. Further, a storage region that resides in a hardwareresource, such as a memory, can be used as needed when informationprocessing is carried out by reading the computer program into theprocessor. Further, the computer program can be installed in thecomputer from a CD-ROM or other such recording medium, or downloaded tothe computer via a communication network.

One embodiment of the present invention will be explained in detailbelow while referring to the Figures. Furthermore, in explaining thisembodiment, sentences having computer program as the subject actuallysignify that processing is being carried out by the CPU, which isexecuting this computer program.

FIG. 1 is a diagram showing an example of the constitution of a computersystem related to this embodiment.

A plurality of hosts 1, a storage system 2, and a host informationmanagement server 3 are connected to each of a first communicationnetwork 4 and a second communication network 5. A variety of networks(for example, a LAN (Local Area Network)) can be used as the firstcommunication network 4. A variety of networks (for example, a SAN(Storage Area Network)) can be used as the second communication network5. Further, the first and second communication networks 4, 5 can also bea single network.

The host 1 is a computer, which accesses a logical volume (logical VOL)22 provided by the storage system 2. The host 1, for example, comprisesa CPU 11; memory 12; HBA (Host Bus Adapter) 14, which is an interfacefor connecting to the storage system 2; and a management I/F (interface)13, which is an interface for connecting to the host informationmanagement server 3. The memory 12, for example, stores a prescribedapplication program (AP) 121, which carries out access to the logicalVOL 22 provide by the storage system 2; an OS (Operating System) 122;and a path manager 123. The process carried out by the path manager 123will be explained in detail hereinbelow.

The storage system 2, for example, can be configured as a RAID(Redundant Arrays of Independent (or Inexpensive) Disks) system,comprising a large number of storage devices (for example, hard diskdrives (HDD)) arranged in an array. The storage device is not limited toHDD, but rather can comprise other types of storage devices, (forexample, flash memory drives), or can be a mixture of a plurality oftypes of storage devices.

The configuration of the storage system will be explained be referringto FIG. 2. As a controller 21, for example, the storage system 2comprises a CHA (Channel Adapter) 211, DKA (Disk Adapter) 218, switch215, shared memory 216, cache memory (hereinafter simply referred to as“cache”) 217, and a management I/F 212, which is the interface forconnecting to the host information management server 3. Access to astorage device 23 is controlled by the storage system 2 controller 21.Furthermore, for example, the functions of the storage system 2controller 21 can be provided in an FC (Fibre Channel) switchconstituting the second communication network 5, and the storage system2 can be realized by combining this FC switch with a plurality ofstorage devices 23.

The CHA 211 is for carrying out data communications with the host 1, andcomprises one or a plurality of communication ports 214. The CHA 211 isconfigured as a microcomputer system (for example, a circuit board),which comprises a CPU and a memory. The memory of the CHA 211, forexample, stores a path creation controller 213. The path creationcontroller 213 is a computer program for creating a path inside thestorage system 2 (a path from the port 214 to the logical volume 22) inaccordance with an indication from the host information managementserver 3. The CHA 211, for example, upon receiving a write command fromthe host 1, respectively writes the write-targeted data to the cachememory 217, and writes the command received from the host 1 to theshared memory 216. Further, when there is a read command from the host1, the CHA 211 writes the command received from the host 1 to the sharedmemory 216, and sends to the host 1 the read-targeted data, which theDKA 218 has read out from the storage device 23 and written to the cache217.

The DKA 218 is for carrying out data communications with the respectivestorage devices 23. The respective DKA 218 can be configured asmicrocomputer systems comprising a CPU and a memory, just like the CHA211. The DKA 218, for example, writes write-targeted data, which hasbeen written to the cache 217 from the CHA 211, to the storage device23, and writes read-targeted data read out from the storage device 23 tothe cache 217.

The switch 215, for example, is a crossbar switch, and is a device,which interconnects the CHA 211, DKA 218, shared memory 216, cache 217,and management I/F 212. Instead of the switch 215, a bus or other typeof connector can also be used.

The shared memory 216, for example, can be configured from either anon-volatile or volatile semiconductor memory. The shared memory 216,for example, stores various types of commands received from the host 1,and control information and the like used to control the storage system2. The commands, control information and the like can be storedredundantly using a plurality of shared memories 216.

The cache 217, for example, can be configured from either a volatile ora non-volatile semiconductor memory. The cache 217 stores data receivedfrom the host 1, and data read out from the storage device 23.Furthermore, the shared memory 216 and cache 217 can be configured asrespectively individual memories as in this embodiment, or can beconfigured as a single memory. When configured as a single memory, forexample, one part of the memory is used as the cache area, and the otherpart of the same memory is used as the shared memory area.

Further, in the storage system 2, for example, one or more RAID groups24 are configured from a plurality of storage devices 23. The RAID group24, for example, provides a redundant storage mode based on RAID 1 orRAID 5. The logical VOL 22 is created by allocating one portion each ofthe respective storage areas of the plurality of storage devices 23 ofthe RAID group 24. The logical VOL 22 is provided to the host 1 from thestorage system 2.

Returning to FIG. 1, the management server 3 is a computer for managingthe host 1 and the storage system 2. The management server 3, forexample, comprises a CPU 31, and a memory 32. The memory 32, forexample, stores various types of computer programs, such as a hostinformation acquisition unit 321, HSD registration processor 322, HSDdetection processor 323, VOL residual capacity registration processor324, VOL decision processor 325, AP information registration processor326, AP run status checker 327, and path creation indication unit 328.Furthermore, the memory 32 also stores a variety of tables, such as anHSD management table 329, VOL management table 320, AP run statusmanagement table 32A, and AP run configuration management table 32B. Theprocessing carried out by the various types of computer programs 321,322, 323, 324, 325, 326, 327, 328, and details concerning the varioustypes of tables 329, 320, 32A, 32B will be explained hereinbelow.

The host information management server 3 related to this embodimentcarries out various processes that enable the user of the host 1 to moreeasily create and change an access path when the user is creating a newpath (this access path) from this host 1 to the logical VOL 22 providedby the storage system 2, or when the user is changing the existingaccess path to a newly created access path. For example, the hostinformation management server 3 automatically detects a portion of theparameters of the plurality of parameters required when creating orchanging an access path. Consequently, the user need not input theparameters automatically detected by the host information managementserver 3, making it possible to lessen the parameter-inputting burden.Further, the changing of an access path must be carried out in a statein which the access path targeted for this change is not in use (thatis, a state in which the AP 121 is not accessing the logical VOL 22 thatutilizes this access path). When an access path change is being carriedout, the host information management server 3 determines whether or notthe AP 121, which uses this access path, is accessing the logical VOL22. Then, the host information management server 3 can control theprocess of changing the access path in accordance with the status ofthis AP 121. For example, if the AP 121 is accessing the logical VOL 22,the host information management server 3 exercises control such that theaccess path change is carried out after this access ends.

As the parameters that the user must input when creating or changing anaccess path, for example, there is a parameter for specifying a newlycreated access path, and information showing the host storage domain(hereinafter abbreviated as “HSD”) to which this newly created accesspath belongs. Parameters for specifying a newly created access path caninclude a VOL ID, which shows the logical VOL 22 that constitutes theaccess destination of this access path; the LUN allocated to this accesspath; and a port ID showing the port 214 allocated to this access path.Details concerning the HSD will be explained by referring to FIG. 12.

FIG. 12 is a diagram illustrating an HSD (Host storage Domain).

As shown in this figure, the storage system 2—managed access paths(paths shown by the broken lines in the figure) have been groupedtogether. This access path group (shown by the ellipsoids in the figure)is HSD 6. In the case of this figure, the access path from host A to thelogical VOL 22 “SVO1,” and the access path from host B to the logicalVOL 22 “SVO2” belong to HSD 6A. Further, the respective access pathsfrom host B to logical VOL 22 “SVO3,” “SVO4,” and “SVGS” belong to HSD6B. A host mode, which corresponds one-to-one with the OS type of OS 122operating in the host 1, is associated with HSD 6. In this figure, hostmode A, which is mapped to the OS type called “OS-A,” is associated withHSD 6A, and host mode B, which is mapped to the OS type called “OS-B,”is associated with HSD 6B. The host modes associated with HSD 6 restrictthe hosts 1 that utilize the access paths belonging to this HSD 6. Thatis, only a host 1, which comprises the OS type OS 122 that is mapped toa host mode associated with HSD 6 can utilize the access paths belongsto this HSD 6. In this figure, the OS type of the OS 122 of both host Aand host C is “OS-A.” Therefore, host A and host C can utilize theaccess paths belonging to HSD 6A, to which host mode A, which is mappedto “OS-A,” is associated. Conversely, since the OS type of the OS 122 ofhost B is “OS-B,” host B is not able to utilize the access pathsbelonging to HSD 6A. In other words, the access paths utilized by hostsA and C are configured so as to belong to the HSD 6 to which the“OS-A”-mapped host mode A is associated. Similarly, the access pathsutilized by host B are configured so as to belong to the HSD 6 to whichthe “OS-B”-mapped host mode B is associated. In accordance with theabove, the storage system 2 is able to control access from the host 1 tothe logical VOL 22 in accordance with the OS type of the OS 122 of thehost 1.

Next, the various types of tables of the host information managementserver 3 (HSD 6 management table 329, VOL management table 320, AP runstatus management table 32A and AP run configuration management table32B) will be explained in detail by referring to FIGS. 3 through 6.Furthermore, in the tables of the respective figures, the attachedreference numerals refer to a column or field, and not to the valuestored in the column or field. Therefore, in the following explanation,a reference numeral will be provided in the explanation when referringto a column or field, but a reference numeral will not be provided inthe explanation when not referring to a column or field.

FIG. 3 is a diagram showing an example of an HSD management table 329.

The HSD management table 329 is for managing the correspondence betweenthe HSD 6, host mode, and OS type. The HSD management table 329, forexample, comprises columns for an HSD 3291, host mode 3292, and OS type3293. The HSD 3291 is the column for storing information (for example,the HSD 6 name and identifier, hereinafter “HSD information”) capable ofuniquely identifying this HSD 6. The host mode 3292 is the column forstoring information (for example, the host mode name and identifier,hereinafter “host mode information”) capable of uniquely identifying thehost mode associated with this HSD 6. The OS type 3293 is the column forstoring the OS type, which is mapped to the host mode associated withthis HSD 6.

FIG. 4 is a diagram showing an example of a VOL management table 320.

The VOL management table 320 is for managing the respective freecapacities (residual capacities) of the logical VOL 22 that the storagesystem 2 is able to provide to the host 1. The VOL management table 320,for example, comprises columns for a VOL ID 3201 and a residual capacity3202. The VOL ID 3201 is the column for storing the identifier of therelevant logical VOL 22 (VOL ID). The residual capacity 3202 is thecolumn for storing the residual capacity of the relevant logical VOL 22.

A value configured in the VOL management table 320 is registered andupdated by a VOL residual capacity registration processor 324. Morespecifically, for example, the VOL residual capacity registrationprocessor 324, either regularly or irregularly, sends to the storagesystem 2 a request for acquiring the residual capacity of the logicalVOL 22 registered in the VOL management table 320, and, if a logical VOL22 has been newly added to the storage system 2, the VOL ID showing thisnewly added logical VOL 22 and the residual capacity of this logical VOL22. Then, the VOL residual capacity registration processor 324 registersin the VOL management table 320 the logical VOL 22 residual capacityreceived from the storage system 2 in response to this request. When theVOL ID showing a newly added logical VOL 22 is notified, the VOLresidual capacity registration processor 324 registers in the VOLmanagement table 320 the information (VOL ID and residual capacity)related to this logical VOL 22.

FIG. 5 is a diagram showing an example of an AP run status managementtable 32A.

The AP run status management table 32A is for managing the run status(the state of access to a logical VOL 22 used by an AP 121) of therelevant AP 121 for each AP 121 running on the host 1. The AP run statusmanagement table 32A, for example, comprises columns for a host 32A1, AP32A2, access state 32A3, and alternative path 32A4. The host 32A1 is thecolumn for storing information (for example, the host name andidentifier, hereinafter the “host information”) capable of uniquelyidentifying the host 1 on which the relevant AP 121 is running. The AP32A2 is the column for storing information (for example, the AP 121 nameand identifier, hereinafter the “AP information”) capable of uniquelyidentifying the relevant AP 121. The access state 32A3 is the column forstoring information showing whether or not it is a state in which therelevant AP 121 is accessing the logical VOL 22 (an access state). Forexample, in access state 32A3, “access” is configured when the relevantAP 121 is currently accessing the logical VOL 22, and “no access” isconfigured when the relevant AP 121 is not accessing the logical VOL 22.The alternative path 32A4 is the column for storing information(hereinafter “alternative path information”) showing whether or notthere is an alternative path for the path (access path) from the host 1to the logical VOL 22 being used by the relevant AP 121. For example,“Yes” is configured in the alternative path 32A4 if an alternative pathexists from the host 1 to the logical VOL 22 used by the relevant AP121, and “No” is configured when the above-mentioned alternative pathdoes not exist.

FIG. 6 is a diagram showing an example of an AP run configurationmanagement table 32B.

The AP run configuration management table 32B is for managing whether ornot the relevant AP 121 is the continuously-running AP for each AP 121running on the host 1. The AP run configuration management table 32B,for example, comprises columns for a host 32B1, AP 32B2, andcontinuously-running 32B3. The host 32B1 and AP 32B2 are the same as thehost 32A1 and AP 32A2 in the AP run status management table 32A. Thatis, the host 32B1 column stores host information on the host 1, which isrunning the relevant AP 121, and the AP 32B2 column stores APinformation on the relevant AP 121. Continuously-running 32B3 is thecolumn for storing information (hereinafter “continuously-runninginformation”) showing whether or not the relevant AP 121 is thecontinuously-running AP. For example, “Yes” is configured incontinuously-running 32B3 when the relevant AP 121 is thecontinuously-running AP, and “No” is configured when the relevant AP 121is not the continuously-running AP.

The preceding is an explanation of the configuration of the computersystem related to this embodiment. The flows of various processescarried out in the host information management server 3, host 1 andstorage system 2 will be explained below. Furthermore, the followingrespective flowcharts show overviews of the respective processes to theextent necessary to understand and implement the present invention.Therefore, a so-called person having ordinary skill in the art will beable to change the order of the steps, or change a step to a differentstep without departing from the scope of the present invention.

FIG. 7 is a flowchart showing the overall flow of processing forcreating a new access path.

This process is started by the user of the host 1 carrying out a newaccess path creation indication to the host 1. When carrying out thisindication, the host 1 user specifies the LUN and port ID to beallocated to a newly created access path.

First, upon receiving the access path creation indication from the user,the host 1 issues an access path creation request to the hostinformation management server 3 (S101). In doing so, the host 1 notifiesthe host information management server 3 of the OS type of the OS 122 ofthe host 1, the AP information of the AP 121 running on the host 1, andthe LUN and port ID specified from the user. Furthermore, the host 1 canalso notify the host information management server 3 of the OS type andAP information beforehand prior to issuing the access path creationrequest. Further, the host information management server 3, uponreceiving the access path creation request, can learn which host 1issued the access path creation request. When the host informationmanagement server 3 can determine the OS type of the OS 122 of this host1, and the AP information of the AP 121 running on this host 1 bydetermining the host 1 that issued this access path creation request,the host 1 does not necessarily have to notify this information (OS typeand AP information) to the host information management server 3. Forexample, the host information management server 3 can determine the OStype and AP information related to the host 1 by maintaining a table formanaging the OS type of the OS 122 of the host 1 and the AP informationof the AP 121 running on the host 1 for each host 1 connected to thestorage system 2.

Having received the access path creation request, the host informationmanagement server 3 carries out a process (hereinafter, “HSD detectionprocess”) for detecting the HSD 6 mapped to the host 1 (hereinafter, the“target host 1”), which issued the access path creation request (S102).The HSD detection process is carried out by an HSD detection processor323. The HSD 6 and the host mode mapped to the target host 1 aredetected by carrying out the HSD detection process, and the HSDinformation and host mode information, which respectively show thedetected HSD 6 and host mode mapped to the target host 1, are notifiedto the path creation indication unit 328. The details of the HSDdetection process will be explained by referring to FIG. 8 hereinbelow.

Next, the host information management server 3 carries out a process(hereinafter the “logical VOL detection process”) for detecting asuitable logical VOL 22 as the logical VOL 22 to be allocated to thenewly created access path (that is, the logical VOL 22, which the AP 121running on the target host 1 will utilize) (S103). The logical VOLdetection process is carried out by the logical VOL detection processor325. The logical VOL 22 to be allocated to a newly created access pathis detected by the logical VOL detection process being carried out, andthe VOL ID, which shows this detected logical VOL 22, is notified to thepath creation indication unit 328. Details of the logical VOL detectionprocess will be explained by referring to FIG. 9 hereinbelow.Furthermore, prior to carrying out the logical VOL detection process, itis desirable that the VOL residual capacity registration processor 324update the value configured in the VOL management table 320 to thenewest value.

Thereafter, the path creation indication unit 328 of the hostinformation management server 3 sends to the storage system 2 an accesspath creation indication, which specifies the parameters (the HSDinformation and host mode information respectively showing the HSD 6 andhost mode mapped to the target host 1 acquired in the HSD detectionprocess of S102, the VOL ID, which shows the logical VOL 22 acquired bythe VOL detection process of S103, and the LUN and port ID specifiedfrom the user) used in creating an access path (S104).

Upon receiving the access path creation indication, the storage system 2uses the parameters specified from the host information managementserver 3 to carry out the creation of an internal path inside thestorage system 2 (a path, which configures an access path, and whichextends from the port 214 to the logical VOL 22) (S105) Morespecifically, for example, the path creation controller 213 of thestorage system 2 executes a command (for example, a command calledAddLUN) for creating an internal path that specifies the VOL ID, LUN andport ID specified from the host information management server 3.Furthermore, for example, when an SCSI (Small Computer System Interface)connection is used instead of an FC connection, a SCSI ID is alsospecified when the internal path creation command is executed.Consequently, an internal path specified by a combination of the VOL ID,LUN and port ID specified from the host information management server 3(a path from the port 214 shown by the port ID to the logical VOL 22shown by the VOL ID) is created. Then, the configuration of theabove-mentioned created internal path is carried out such that thiscreated internal path belongs to the HSD 6, which is shown by the HSDinformation specified from the host information management server 3. Thehost mode shown by the host mode information specified from the hostinformation management server 3 is also used at the time of thisconfiguration.

Subsequent to the creation of the internal path inside the storagesystem 2 ending, the storage system 2 notifies the host informationmanagement server 3 to the effect that internal path creation has ended(S106).

When the host information management server 3 has received the internalpath creation end notification from the storage system 2, the pathcreation indication unit 328 of the host information management server 3sends to the target host 1 an access path creation indication specifyingthe same parameters as the parameters specified in S104 (that is, theHSD information, host mode information, VOL ID, LUN and port ID) (S107).

The target host 1, which receives the access path creation indication,uses the parameters specified from the host information managementserver 3 to carry out the creation of a path connecting to the internalpath that the storage system 2 created in S105 (S108). Morespecifically, the path manager 123 of the target host 1 executes aprescribed command for creating a path connecting to the internal path,which specifies the HSD information, host mode information, VOL ID, LUNand port ID specified from the host information management server 3.Consequently, a path (access path) is created from the target host 1 tothe logical VOL 22 shown by the VOL ID specified from the hostinformation management server 3.

FIG. 8 is a flowchart of an HSD detection process.

First, the HSD detection processor 323 determines whether or not the OStype related to the target host 1 (the OS type notified from the targethost 1 in S101 of FIG. 7) is registered in the HSD management table 329(S201).

When the OS type related to the target host 1 is registered in the HSDmanagement table 329 (S201: YES), the HSD detection processor 323acquires the HSD information and host mode information mapped to thetarget host 1 (mapped to the OS type related to the target host 1) fromthe HSD management table 329 (S202).

Conversely, when the OS type related to the target host 1 is notregistered in the HSD management table 329 (S201: NO), a process, whichacquires the HSD information and host mode information mapped to thetarget host 1 from the storage system 2, and registers same in the HSDmanagement table 329, is carried out (S203, S204). This registrationprocess is carried out by the HSD registration processor 322. Morespecifically, the HSD registration processor 322 sends to the storagesystem 2 a request to acquire the HSD information and host modeinformation mapped to the target host 1. On doing so, the HSDregistration processor 322 notifies the storage system 2 of the OS typerelated to the target host 1. The storage system 2, which receives therequest for acquiring the HSD information and host mode information,detects the HSD 6 and host mode mapped to the OS type notified togetherwith this request. For example, the CHA 211 of the storage system 2manages what host mode and OS type are associated with the HSD 6 foreach HSD 6 by maintaining a mapping table. The storage system 2 candetermine the HSD 6 and host mode associated with the OS type notifiedfrom the host information management server 3 by referencing thismapping table. Thereafter, the storage system 2 notifies the hostinformation management server 3 of the HSD information showing thedetected HSD 6, and the host mode information showing the detected hostmode. The HSD registration processor 322 of the host informationmanagement server 3, which receives the notification of the HSDinformation and host mode information, associates this information withthe OS type of the target host 1, and registers this information in theHSD management table 329.

Thereafter, the HSD detection processor 323 notifies the path creationindication unit 328 of the HSD information and host mode informationacquired in S202 and S203.

FIG. 9 is a flowchart of a logical VOL detection process.

First, the VOL detection processor 325 references the VOL managementtable 320, and detects a suitable logical VOL 22 as the logical VOL 22to be allocated to a newly created access path (that is, the logical VOL22 to be used by the AP 121 running on the target host 1) (S301).Various criteria can be taken into consideration in determining whichlogical VOL 22 to use as the suitable logical VOL 22, but the VOLdetection processor 325, for example, can select any one of thefollowing three criteria to detect a suitable logical VOL 22.

(Criteria 1) Use the logical VOL 22 with the largest residual capacityas the suitable logical VOL 22. That is, in the case of this criteria 1,when there are logical VOL 22 like those shown in FIG. 4, the VOLdetection processor 325 detects the logical VOL 22 having VOL ID “SVO3,”which has the largest residual capacity (“1 TB (terabyte)”) as thesuitable logical VOL 22.

(Criteria 2) A logical VOL 22 capacity deemed the minimum required forutilizing an AP 121 (hereinafter “AP utilization capacity”) is pre-setfor each type of AP of the AP 121 running on the respective hosts 1, andthe logical VOL 22 having the same capacity as this pre-set APutilization capacity, or a capacity in proximity thereof (that is, aresidual capacity that is the same as or close to the above configuredAP utilization capacity) is used as the suitable logical VOL 22.

(Criteria 3) The logical VOL 22 having a capacity that is greater than apre-set threshold is used as the suitable logical VOL 22. When there isa plurality of logical VOL 22 having capacities greater than thethreshold, the logical VOL 22 with the capacity closest to the thresholdis used as the suitable logical VOL 22. The threshold can be configuredby the user, or an average value of the residual capacity of the logicalVOL 22 that can be provided to the host 1 by the storage system 2 may beused as this threshold.

Next, the VOL detection processor 325 determines whether or not asuitable logical VOL 22 was detectable in S301 (S302).

When a suitable logical VOL 22 could be detected (S302: YES), the VOLdetection processor 325 notifies the path creation indication unit 328of the VOL ID of the detected logical VOL 22 (S303).

Conversely, when a suitable logical VOL 22 could not be detected (S302:NO), the VOL detection processor 325 sends an error notification to thiseffect to the target host 1, and ends the access path creation process(S304).

The preceding is an explanation of the process for creating a new accesspath. In accordance with the above process being carried out, the hostinformation management server 3 automatically detects the parametersnecessary for creating an access path, and uses these detectedparameters to create a path (an access path) from the host 1 to thelogical VOL 22 of the storage system 2. Therefore, when carrying outaccess path creation, the user can easily create an access path bysimply specifying parameters other than the parameters automaticallydetected by the host information management server 3 (the LUN and portID in this embodiment).

Furthermore, in this embodiment, the host information management server3 automatically detects the logical VOL 22 to be connected to a newlycreated access path, but it is not always necessary to do this. When theuser wants to decide the logical VOL 22 to be allocated to a newlycreated access path, for example, the user can specify the VOL IDshowing the logical VOL 22 when the user issues an indication to thehost 1.

FIG. 10 is a flowchart showing the overall flow of processing forchanging an existing access path to a newly created access path.

Of the respective steps comprising this process, the same symbols as thesymbols used in FIG. 7 will be assigned to the steps that carry outsubstantially the same processing as those of FIG. 7. In the explanationof FIG. 10, the points of difference with FIGS. 7 through 9 will mainlybe explained.

The process of FIG. 10 is started by the host 1 user carrying out anindication to the host 1 to change the existing access path. Whencarrying out this indication, the host 1 user specifies the VOL ID, LUNand port ID that specify the change-targeted access path.

First, the processing of S101 through S103 is carried out in the host 1and host information management server 3. That is, the host 1 issues arequest to the host information management server 3 to change the accesspath (S101). In so doing, in addition to notifying the OS type, APinformation, LUN and port ID to the host information management server 3the same as the case of FIG. 7, the host 1 also notifies the hostinformation management server 3 of the VOL ID specified from the user(the VOL ID showing the logical VOL 22 allocated to the pre-changeaccess path). In the explanation of FIG. 10, the host 1 that issues theaccess path change request to the host information management server 3will be called the “target host 1.”

The host information management server 3, which receives the access pathchange request, carries out an HSD detection process for detecting theHSD 6 and host mode mapped to the target host 1, which is used whencreating and changing the access path (S102). The HSD detection processis substantially the same as the process explained using FIG. 8.Further, the host information management server 3 carries out a logicalVOL detection process for detecting the logical VOL 22 to be allocatedto the post-change access path (S103). The logical VOL detection processis substantially the same as the process explained using FIG. 9.

Next, the host information management server 3 carries out a process(hereinafter the “AP run status check process”) for checking the runstatus of the AP 121 running on the target host 1 (S401). The AP runstatus check process is carried out by the AP run status checker 327.Carrying out the AP run status check process determines whether or notthe AP 121 running on the target host 1 is in the process of accessingthe logical VOL 22 (in other words, whether or not the change-targetedaccess path is currently in use). For example, if the status of the AP121 is access-in-progress, or if this AP is the continuously-running AP121, the host information management server 3 transitions to standbyuntil this access ends. Then, after this access ends, the hostinformation management server 3 issues an indication to the storagesystem 2 and target host 1 to change the access path. Details concerningthe AP run status check process will be explained hereinbelow byreferring to FIG. 11.

Thereafter, the path creation indication unit 328 of the hostinformation management server 3 determines whether or not an alternativepath will be used when changing the access path (S402). Morespecifically, in the AP run status check process, when a notification tothe extent that an alternative path will be used is received from the APrun status checker 327, the path creation indication unit 328 determinesto utilize an alternative path, and when the above-mentionednotification is not received, the path creation indication unit 328determines not to utilize an alternative path.

When an alternative path is not utilized (S402: NO), the path creationindication unit 328 implements the processing of S104.

Conversely, when an alternative path is utilized (S402: YES), the pathcreation indication unit 328 indicates to the target host 1 to switchthe access path (S403).

The path manager 123 of the target host 1, which receives the accesspath switch indication, notifies the host information management server3 to the extent that the access path was switched to the alternativepath, and this switchover has ended (S404).

Thereafter, the processing of S104 through S108 is carried out the sameas the processing of FIG. 7. Consequently, a path (access path) from thetarget host 1 to the logical VOL 22 of the storage system 2 is newlycreated using the parameters (LUN and port ID) specified from the user,and the parameters (HSD information, host mode information, and VOL ID)automatically detected by the host information management server 3. Inso doing, the existing access path is changed to the newly createdaccess path.

Upon receiving the notification from the target host 1 that access pathcreation has ended (S405), the path creation indication unit 328 of thehost information management server 3 determines whether or not analternative path was utilized when the access path change was carriedout (S406).

When an alternative path was not utilized (S406: NO), the path creationindication unit 328 ends the access path change process.

When an alternative path was utilized (S406: YES), the path creationindication unit 328 indicates to the target host 1 to switch from thealternative path to the newly created access path (S407).

The path manager 123 of the target host 1, which receives the accesspath switch indication, switches the access path from the alternativepath to the newly created access path (S408).

FIG. 11 is a flowchart of an AP run status check process.

First, the AP run status checker 327 acquires from the storage system 2the run status of the AP 121 (hereinafter, the “target AP 121”) runningon the target host 1, and registers this result in the AP run statusmanagement table 32A (S501). More specifically, the AP run statuschecker 327 queries the storage system 2 as to whether or not thelogical VOL 22 shown by the VOL ID notified in S141 (the VOL ID of thelogical VOL 22 utilized by the AP 121 running on the target host 1) isbeing accessed from the target AP 121 (access-in-progress status). Whenthe result of this query is the access-in-progress status, the AP runstatus checker 327 configures “access” in the access status 32A3 mappedto the target AP 121 in the AP run status management table 32A.Conversely, when the result is not the access-in-progress status, the APrun status checker 327 configures “no access” in the access status 32A3mapped to the target AP 121 in the AP run status management table 32A.Furthermore, the target AP 121 is the AP 121 shown by the AP informationnotified in S101.

Next, the AP run status checker 327 references the AP run statusmanagement table 32A, and determines whether or not the target AP 121 isin the access-in-progress status (S502).

When the target AP 121 is not in the access-in-progress status (S502:NO), the AP run status checker 327 ends the AP run status check process.

Conversely, when the target AP 121 is in the access-in-progress status(S502: YES), the AP run status checker 327 determines whether or not thecontinuously-running information related to the target AP 121 isregistered in the AP run configuration management table 32B (S503).

When the continuously-running information related to the target AP 121is registered in the AP run configuration management table 32B (S503:YES), the AP run status checker 327 acquires the continuously-runninginformation related to the target AP 121 from the AP run statusmanagement table 32B (S504).

Conversely, when the continuously-running information related to thetarget AP 121 is not registered in the AP run configuration managementtable 32B (S503: NO), a process is carried out for acquiring thecontinuously-running information related to the target AP 121 from thetarget host 1, and registering this continuously-running informationrelated to the target AP 121 in the AP run configuration managementtable 32B (S505, S506). This registration process is carried out by theAP information registration processor 326. More specifically, the APinformation registration processor 326 sends to the target host 1 arequest for acquiring the continuously-running information related tothe target AP 121. The target host 1, which receives the request foracquiring the continuously-running information, checks whether or notthe target AP 121 is the continuously-running AP, and notifies the hostinformation management server 3 of this result as thecontinuously-running information. The AP information registrationprocessor 326 of the host information management server 3, whichreceives this continuously-running information notification, associatesthe notified continuously-running information with the AP information ofthe target AP 121, and registers this information in the AP runconfiguration management table 32B.

Thereafter, the AP run status checker 327 references thecontinuously-running information acquired in S504 and S505, anddetermines whether or not the target AP 121 is the continuously-runningAP 121 (S507).

When the target AP 121 is not the continuously-running AP 121 (S507:NO), the AP run status checker 327 transitions to standby until theaccessing of the logical VOL 22 by the target AP 121 ends. Then, afterthe accessing of the logical VOL 22 by the target AP 121 has ended, theAP run status checker 327 ends the standby of S508, and ends the AP runstatus check process.

Conversely, when the target AP 121 is the continuously-running AP 121(S507: YES), the AP run status checker 327 determines whether or not thealternative path information related to the target AP 121 is registeredin the AP run status management table 32A (S509).

When the alternative path information related to the target AP 121 isregistered in the AP run status management table 32A (S509: YES), the APrun status checker 327 acquires the alternative path information relatedto the target AP 121 from the AP run status management table 32A (S510).

Conversely, when the alternative path information related to the targetAP 121 is not registered in the AP run status management table 32A(S509: NO), a process is carried out for acquiring the alternative pathinformation related to the target AP 121 from the target host 1, andregistering this acquired alternative path information related to thetarget AP 121 in the AP run status management table 32A (S511, S512).This registration process is carried out by the AP informationregistration processor 326, and is substantially the same as the processfor registering the continuously-running information (S505, S506). Thatis, the AP information registration processor 326 sends to the targethost 1 a request to acquire the alternative path information related tothe target AP 121. The target host 1, which receives the request toacquire the alternative path information, checks whether or not analternative path exists for the path (access path) from the target host1 to the logical VOL 22 utilized by the target AP 121, and notifies theresult thereof to the host information management server 3 as thealternative path information. The AP information registration processor326 of the host information management server 3, which receives thealternative path information notification, associates the notifiedalternative path information with the AP information of the target AP121, and registers this alternative path information in the AP runstatus management table 32A.

Thereafter, the AP run status checker 327 references the alternativepath information acquired in S510 and S511, and determines whether ornot an alternative path related to the target AP 121 (an alternativepath of the access path from the target host 1 to the logical VOL 22utilized by the target AP 121) exists (S513).

When an alternative path related to the target AP 121 does not exist(S513: NO), the AP run status checker 327 sends an error notification tothis effect to the target host 1, and ends the access path changeprocess (S514).

Conversely, when an alternative path related to the target AP 121 doesexist (S513: YES), the AP run status checker 327 notifies the pathcreation indication unit 328 to the effect that an alternative path willbe utilized when the access path change is carried out, and ends the APrun status check process. As described hereinabove, when an alternativepath is utilized, the process of changing to the access path is carriedout after switching the access path currently being used by the targetAP 121 (that is, the change-targeted access path) to the alternativepath.

The preceding is an explanation of the process for changing an existingaccess path to a newly created access path. By carrying out the aboveprocess, the host information management server 3 can control the host 1and the storage system 2 such that the access path change process iscarried out in a state in which this access path is not being used (astate in which the AP 121 is not using this access path to access thelogical VOL 22). More specifically, the host information managementserver 3 exercises control such that if the AP 121 is accessing thelogical VOL 22, the access path change is carried out subsequent to thisaccess ending. Further, when the AP 121 status is access-in-progress,this AP is the continuously-running AP 121, and there is an alternativepath related to this AP 121, the host information management server 3exercises control such that access path change is carried out afterswitching to the alternative path (that is, after the status becomessuch that the change-targeted access path is not in use) Consequently,the user can start the access path change process without having to beespecially conscious of whether or not the change-targeted access pathis currently in use.

The numerous embodiments of the present invention described hereinaboveare examples for explaining the present invention, and do not purport tolimit the scope of the present invention solely to these embodiments.The present invention can be put into practice in a variety of othermodes without departing from the gist thereof.

1. A path creation support apparatus for supporting the creation of anaccess path from a host to a logical volume in a storage system, aplurality of the access paths being grouped together on the basis of thetype of operating system (OS) of the host that utilizes the access path,the path creation support apparatus comprising: a group informationacquisition unit for acquiring group information from the storagesystem, the group information showing the group to which the access pathutilized by the host belongs; a group information storage unit forstoring the acquired group information and the type of OS of the host,which is associated with the acquired group information; a path creationindication unit configured to: receive an access path creation startrequest; acquire group information from the group information storageunit, the group information associated with the type of OS of the hostwhich is to carry out the access path creation; and send an access pathcreation indication to the host and the storage system, the access pathcreation indication specifying a parameter together with the access pathcreation start request and the acquired group information; a logicalvolume information acquisition unit for acquiring logical volumeinformation from the storage system, the logical volume informationshowing respective logical volumes that can be provided to the host bythe storage system and the residual capacities of the respective logicalvolumes; a logical volume information storage unit for storing theacquired logical volume information and the residual capacities of thelogical volumes associated with the acquired logical volume information;and a host storage domain (HSD) device configured to acquire and saveHSD information and application program operational information used inan access path change process.
 2. The path creation support apparatusaccording to claim 1, further comprising: a logical volume decision unitfor deciding a logical volume to be allocated to a created access pathbased on the residual capacities of the respective logical volumesstored in the logical volume information storage unit, wherein theaccess path creation indication further specifies logical volumeinformation showing the logical volume decided by the logical volumedecision unit.
 3. The path creation support apparatus according to claim2, wherein the logical volume decision unit decides the logical volumefor which the logical volume residual capacity is the largest of thelogical volumes stored in the logical volume information storage unit asthe logical volume to be allocated to a created access path.
 4. The pathcreation support apparatus according to claim 2, wherein the logicalvolume decision unit decides the logical volume for which the logicalvolume residual capacity is the closest to a pre-set threshold of thelogical volumes stored in the logical volume information storage unit asthe logical volume to be allocated to a created access path.
 5. The pathcreation support apparatus according to claim 1, wherein the access pathcreation start request is a request to start the change of the accesspath and the path creation support apparatus further comprises: anapplication information acquisition unit for acquiring accessinformation from the host, the access information showing whether or notan application, which runs on the host and uses the access path toaccess a logical volume, is accessing the logical volume by utilizing achange-targeted access path, and continuously-running informationshowing whether or not the application is running continuously; anapplication information storage unit for storing the access informationand the continuously-running information associated with theapplication; and a path-change-time decision unit which, upon receipt ofan access path change start request: references the access informationand the continuously-running information associated with the applicationrunning on the host that is to carry out the access path change; whenthe application is accessing the logical volume by utilizing thechange-targeted access path and the application is not thecontinuously-running application, stands by until the accessing of thelogical volume by the application utilizing the change-targeted accesspath ends; and causes the path creation indication unit to carry out anaccess path change indication subsequent to the end of the accessing ofthe logical volume utilizing the change-targeted access path.
 6. Thepath creation support apparatus according to claim 1, wherein the accesspath creation start request is a request to start the change of theaccess path and the path creation support apparatus further comprises:an application information acquisition unit for acquiring accessinformation from the host, the access information showing whether or notan application, which runs on the host and uses the access path toaccess the logical volume, is accessing the logical volume by utilizinga change-targeted access path, continuously-running information showingwhether or not the application is running continuously, and alternativepath information showing whether or not there is an alternative path forthe access path utilized by the application; an application informationstorage unit for storing the access information, thecontinuously-running information, and the alternative path informationassociated with the application; and an alternative path switchoverindication unit which, upon receipt of an access path change startrequest: references the access information, the continuously-runninginformation, and the alternative path information associated with theapplication running on the host that is to carry out the access pathchange; when the application is accessing the logical volume byutilizing the change-targeted access path, the application is thecontinuously-running application, and there is an alternative path tothe change-targeted access path, causes the path creation indicationunit to carry out an access path change indication subsequent toindicating to the host to switch the access path from thechange-targeted access path to the alternative path; and indicates tothe host to switch the access path from the alternative path to apost-change access path subsequent to the access path change ending. 7.A path creation support method for supporting the creation of an accesspath from a host to a logical volume in a storage system, a plurality ofthe access paths being grouped together on the basis of the type ofoperating system (OS) of the host that utilizes the access path, thepath creation support method comprising the steps of: acquiring groupinformation from the storage system, the group information showing thegroup to which the access path utilized by the host belongs; storing theacquired group information and the type of OS of the host, which isassociated with the acquired group information; upon receipt of anaccess path creation start request: acquiring group informationassociated with the type of OS of the host which is to carry out theaccess path creation; and sending an access path creation indication tothe host and the storage system, the access path creation indicationspecifying a parameter together with the access path creation startrequest and the acquired group information; acquiring logical volumeinformation from the storage system, the logical volume informationshowing respective logical volumes that can be provided to the host bythe storage system and the residual capacities of the respective logicalvolumes; storing the acquired logical volume information and theresidual capacities of the logical volumes associated with the acquiredlogical volume information; acquiring host storage domain (HSD)information and application program operational information; and storingthe acquired HSD information and application program operationalinformation.
 8. The path creation support method according to claim 7,further comprising the steps of: deciding a logical volume to beallocated to a created access path based on the residual capacities ofthe respective logical volumes stored in the logical volume informationstorage unit; and specifying logical volume information showing thedecided logical volume by means of the access path creation indication.9. The path creation support method according to claim 8, furthercomprising the step of: deciding the logical volume for which thelogical volume residual capacity is the largest of the stored logicalvolumes as the logical volume to be allocated to a created access path.10. The path creation support method according to claim 8, furthercomprising the step of: deciding the logical volume for which thelogical volume residual capacity is the closest to a pre-set thresholdof the stored logical volumes as the logical volume to be allocated to acreated access path.
 11. The path creation support apparatus accordingto claim 7, wherein the access path creation start request is a requestto start the change of the access path and the path creation supportmethod further comprises the steps of: acquiring access information fromthe host, the access information showing whether or not an application,which runs on the host and uses the access path to access a logicalvolume, is accessing the logical volume by utilizing a change-targetedaccess path, and continuously-running information showing whether or notthe application is running continuously; storing the access informationand the continuously-running information associated with theapplication; and upon receipt of an access path change start request:referencing the access information and the continuously-runninginformation associated with the application running on the host that isto carry out the access path change; when the application is accessingthe logical volume by utilizing the change-targeted access path and theapplication is not the continuously-running application, standing byuntil the accessing of the logical volume by the application utilizingthe change-targeted access path ends; and carrying out an access pathchange indication subsequent to the end of the accessing of the logicalvolume utilizing the change-targeted access path.
 12. The path creationsupport method according to claim 7, wherein the access path creationstart request is a request to start the change of the access path andthe path creation support method further comprises the steps of:acquiring access information from the host, the access informationshowing whether or not an application, which runs on the host and usesthe access path to access the logical volume, is accessing the logicalvolume by utilizing a change-targeted access path, continuously-runninginformation showing whether or not the application is runningcontinuously, and alternative path information showing whether or notthere is an alternative path for the access path utilized by theapplication; storing the access information, the continuously-runninginformation, and the alternative path information associated with theapplication; and upon receipt of an access path change start request:referencing the access information, the continuously-runninginformation, and the alternative path information associated with theapplication running on the host that is to carry out the access pathchange; when the application is accessing the logical volume byutilizing the change-targeted access path, the application is thecontinuously-running application, and there is an alternative path tothe change-targeted access path, carrying out an access path changeindication subsequent to indicating to the host to switch the accesspath from the change-targeted access path to the alternative path; andindicating to the host to switch the access path from the alternativepath to a post-change access path subsequent to the access path changeending.